Deep ocean circulation plays a key role in climate, with surface currents transporting heat from the tropics to the sub-polar latitudes, and the deep ocean acting as a reservoir of carbon. Data suggest large-scale re-organisations of ocean circulation occurred on glacial-interglacial periods as well as millennial timescales, with data and models suggesting a strong link with global climate changes. Although we have techniques to reconstruct past deep ocean chemistry and biology, the past physics of ocean circulation and turbulent mixing is unexplored because there are no tools which we can use to reconstruct it. The marine lithic archive is ubiquitous and encapsulates information which can transform our knowledge about past changes in the physics of ocean circulation and its role in climate change. The central idea of this PhD studentship is to link the dispersion and sorting of marine sediment by deep ocean advection to quantify deep ocean current velocities and turbulent mixing using fluid dynamic modelling and experimental measurements.

Project summary:

This PhD project is focused on unlocking the primary oceanographic variables which are encoded into the marine sedimentary record. Coupled measurements of geochemistry across grain-sizes constrain the sources-to-sink dispersion of sediment particles by deep ocean currents. This studentship will seek to quantitatively develop this technique into a novel palaeo-proxy with which we can reconstruct past oceanographic dynamics. Fluid dynamic modelling and experiments will simulate marine sediment dispersion under varying deep ocean current flow speeds, density stratification, and rates of turbulent mixing. Modelling of sediment dispersion by ocean currents will provide insight into some of the key relations between sediment deposition patterns and the conditions driving ocean circulation in the modern and geological past.

What the student will do:

The student will develop a process-type model to describe the spatial supply of sediment to a deep ocean current, its transport, and ensuing sedimentation. Multiple variables will be explored including changes in the sources and concentrations of sediment, particle grain size distributions, particle chemical reactability, as well as ocean water mass vertical stratification, advection speeds, and turbulent mixing. The student will also model the deposition which arises from intermittent particle input to understand millennial-scale changes such as Heinrich Events. In addition to mathematical modelling, we will build on recent non-invasive experimental measurements of mixing, conducted at the BP Institute, in which the mixing can be measured from light attenuation of dye. These will provide an ideal analogue to test the process models of sediment mixing, transport and deposition.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

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